JP2015055779A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to improve development efficiency and transfer efficiency, while enabling stable high-quality image output.SOLUTION: The image forming apparatus forms an image on a recording medium by use of liquid developer. The liquid developer is formed by dispersing toner particles in an insulating liquid. An average circularity of the toner particle is 0.90 or more and 0.98 or less. The image forming apparatus includes: a first toner carrier carrying the toner particles on a surface; a second toner carrier arranged opposite the first toner carrier and carrying the toner particles on a surface; and a power supply device for applying an electric field between the first and second toner carriers. The first toner carrier has a resistive layer formed on its surface. Electric resistance per unit area of the resistive layer is 10Ω cmor more and 10Ω cmor less.

Description

  The present invention relates to an image forming apparatus. More specifically, the present invention relates to an image forming apparatus that forms an image using a liquid developer.

  An electrophotographic image forming apparatus such as a copying machine, a printer, a digital printing machine, and a simple printing machine has been widely used. Among these, there is also a wet image forming apparatus that uses a liquid developer as a developer (see, for example, JP-A-2009-096994 (Patent Document 1)).

JP 2009-096994 A

  The liquid developer is a developer in which toner particles containing a colorant and the like are dispersed in an insulating liquid (also referred to as a carrier liquid). Various types of such liquid developers are known, but the current mainstream is a liquid developer using pulverized toner particles.

  The pulverized toner particles are toner particles that are made into fine particles by previously melt-kneading a resin and a colorant and then pulverizing them in a dry state or a wet state in a carrier liquid. In general, the shape of the pulverized toner particles is difficult to control, and the particle shape tends to be indefinite. For this reason, when an image is formed using a liquid developer containing pulverized toner particles, for example, in the transfer process, the adhesion between the transfer roll carrying the toner particles and the toner particles becomes excessively strong, and recording is performed from the transfer roll. In some cases, the toner particles cannot smoothly move to the medium, causing problems such as unstable image density. For the same reason, an image forming apparatus using a liquid developer containing pulverized toner particles has certain limits on development efficiency and transfer efficiency.

  Further, in recent years, it has been desired to reduce the particle size of toner particles. This is because by reducing the toner particles, the amount of toner adhered during printing can be reduced, which improves the image quality and reduces the environmental burden. In order to contribute to this purpose, the particle size of the toner particles is preferably about 0.5 to 2 μm. However, there has been a problem that enormous energy and cost are required to realize such a particle size by pulverization.

  In recent years, for example, as disclosed in Patent Document 1, a production method advantageous for reducing the particle size of toner particles has been developed and attracted attention. This method is classified as a granulation method, in which the toner particles are composed of a core / shell structure by two different resins. Specifically, the core resin is dissolved in a good solvent to obtain a resin solution, and this resin solution is mixed with an interfacial tension modifier (shell resin fine particles) and sheared with a poor solvent having an SP value different from that of the good solvent. After forming droplets, the good solvent is volatilized to form resin fine particles.

  According to this method, the particle size and shape of the toner particles can be highly controlled by appropriately adjusting the shearing method, the interfacial tension difference, or the interfacial tension adjusting agent (shell resin). Further, the cost required for reducing the particle size of the toner particles is lower than that of the pulverization method.

  By using the method as described above, it is possible to make the shape of the toner particles not an indefinite shape but a shape close to a sphere (in other words, a high degree of circularity). As a result, problems such as image density instability caused by irregular shaped particles have been partially solved, and further improvement in transfer efficiency has been expected.

  However, when an image is formed using toner particles having such a high degree of circularity, a new problem has arisen that minute image noise is generated, image density is lowered, and density unevenness is caused.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an image forming apparatus that has high development efficiency and transfer efficiency and can stably output a high-quality image. It is to provide.

  In order to solve the above problems, the present inventor has investigated in detail image noise and density unevenness generated in a solid image portion (also referred to as a solid image portion) in an image transferred to a recording medium. Then, in the solid image portion, it has been found that the toner particles are not uniformly adhered, and the toner particles are unevenly distributed and adhered in a dot shape with a constant period of about several tens of μm. The following image noise is referred to as “granular unevenness”. The present inventor stopped the image forming apparatus during the image formation process and checked the state of the image in each part of the apparatus in order to identify the cause of the occurrence of the granular unevenness. It has become clear that this has already occurred.

  As a result of further detailed investigation, it was found that this granular unevenness occurs by the following mechanism. At the upstream side of the development nip (the part where the development roll and the photosensitive drum are in contact with each other via the liquid developer), the charged toner particles begin to be affected by the development electric field and electrostatically move from the development roll to the photosensitive drum. Start moving. At this time, if the moving speed of the toner particles is sufficiently slow and the timing at which the toner particles reach the surface of the developer layer (carrier liquid) is after the nip portion has entered, no granular unevenness occurs. However, when the movement speed of the toner particles is high and the toner particles reach the surface of the developer layer before entering the nip portion, granular unevenness occurs.

  The toner particles that have reached the surface of the carrier liquid before entering the nip portion still move by the action of the electric field. Therefore, the liquid level is pushed up by the toner particles. However, the amount of the carrier liquid is limited and does not exist to fill the space before the development nip. Accordingly, the liquid level is not uniform and is pushed up so as to sparsely swell at a certain period. That is, irregularities are generated on the surface of the carrier liquid. Then, the toner particles tend to be closer to the photosensitive drum by the action of the electric field, so that the toner particles are unevenly distributed on the convex portion generated on the liquid surface. As a result, a portion where the toner particles are dense and a portion where the toner particles are sparse appear periodically, and granular unevenness occurs.

  When granular unevenness occurs, the solid portion of the image includes a portion that is not covered with toner particles. Therefore, compared to the case where no unevenness of granularity occurs, even if toner particles with the same adhesion amount are developed or transferred, the average image density is reduced, the density is recognized as unevenness, or the gloss of the image Deterioration of the image quality is caused, for example, the degree of image quality decreases and the feeling of rustling becomes apparent.

  Based on the above knowledge, the present inventor considers that the cause of the occurrence of granular unevenness is the mobility (ease of movement) of the toner particles, and not only the development process but also the electrostatic discharge of the toner particles between the roll members. It was speculated that granular unevenness may occur at locations where delivery is performed. Then, when individual experiments were performed simulating the primary transfer process and the secondary transfer process, the granular unevenness was reproduced as expected.

  The mobility of toner particles is greatly affected by the particle shape. In other words, irregular toner particles have a low moving speed, and toner particles having a high degree of circularity have a high moving speed. Therefore, the granular unevenness is considered to be a problem peculiar to toner particles having a high degree of circularity. In order to limit the moving speed of the toner particles, for example, it is conceivable to increase the viscosity of the carrier liquid. However, if the viscosity of the liquid developer is increased more than necessary, each apparatus for stirring and liquid feeding can be used. Since the applied load becomes large, it is not preferable.

  Therefore, as a result of intensive studies on a method for suppressing the movement speed of the toner particles without depending on such means, the present inventor has controlled the resistance of a specific member of the image forming apparatus, and thereby has a high degree of circularity. The present inventors have found that the moving speed of particles can be limited and have completed the present invention.

In other words, the image forming apparatus of the present invention is an image forming apparatus that forms an image on a recording medium using a liquid developer, and the liquid developer has toner particles dispersed in an insulating liquid. The average circularity of the toner particles is 0.90 or more and 0.98 or less, and the first toner carrier that supports the toner particles on the surface thereof is disposed opposite to the first toner carrier. A second toner carrier that carries the toner particles on the surface, and a power supply device that applies an electric field between the first toner carrier and the second toner carrier. The toner carrier has a resistance layer on its surface, and the electrical resistance per unit area of the resistance layer is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less.

  Here, the toner particles have a core / shell structure in which a shell resin is attached to or coated on the surface of the core resin, the shell resin includes a vinyl resin, and the vinyl resin is included in a side chain. It preferably has a long hydrocarbon chain.

  The core resin is a urethane-modified polyester resin in which two or more polyester components are bonded by a structural unit derived from a compound having an isocyanate group, and the polyester component is derived from an aliphatic monomer in the molecular structure. It is preferable that the structural unit including the structural unit and derived from the aliphatic monomer occupies 80% or more of the total structural unit in the polyester component.

  In addition, the image forming apparatus is disposed as the first toner carrier, the developer carrier, and the second toner carrier as opposed to the developer carrier. It is preferable to include an image carrier that is developed by the toner particles carried thereon and forms a toner image on the surface.

The image forming apparatus includes, as a third toner carrier, an intermediate transfer member that is disposed to face the image carrier and to which a toner image formed on the surface of the image carrier is transferred. A power supply device that applies an electric field between the transfer member and the image carrier, and the intermediate transfer member has a resistance layer on a surface thereof, and the electric resistance per unit area of the resistance layer is It is preferably 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less.

The image forming apparatus further includes a transfer support member disposed on the opposite side of the image carrier with the recording medium interposed therebetween, and the transfer support member has a resistance layer on a surface thereof, and the resistance layer The larger of the electrical resistance per unit area and the electrical resistance per unit area of the recording medium is preferably 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less.

The image forming apparatus further includes a transfer support member disposed on the opposite side of the intermediate transfer body with the recording medium interposed therebetween, and the transfer support member has a resistance layer on a surface thereof, and the intermediate transfer Of the electrical resistance per unit area of the resistance layer of the body, the electrical resistance per unit area of the resistance layer of the transfer support member, and the electrical resistance per unit area of the recording medium, the largest value is 10 ^5. It is preferably Ω · cm ² or more and 10 ⁸ Ω · cm ² or less.

  Further, the toner carrier and the transfer support member include a base material and a resistance layer provided on the base material, and the resistance layer includes a plurality of layers, and the outermost surface layer of the plurality of layers. Preferably has the highest electrical resistance value among the layers included in the plurality of layers.

  The image forming apparatus of the present invention has high development efficiency and transfer efficiency, and can stably output a high-quality image.

1 is a schematic cross-sectional view illustrating an example of an image forming apparatus according to an exemplary embodiment. It is a figure for demonstrating the experimental condition of the experiment example regarding this Embodiment. It is a figure which shows an example of the experimental result of the experiment example regarding this Embodiment.

  Hereinafter, embodiments according to the present invention will be described in more detail. In the following, the description may be made with reference to the drawings. However, in the drawings of the present invention, the dimensional relationships such as length, width, thickness, and depth are appropriately changed for the sake of clarity and simplification of the drawings. It does not represent the actual dimensional relationship.

<Image forming apparatus>
The image forming apparatus according to the present embodiment includes a first toner carrier and a second toner carrier, and the first toner carrier and the second toner carrier are disposed to face each other. . Here, “disposed oppositely” means that when the first toner carrier and the second toner carrier are arranged to face each other so as to contact each other, the first toner carrier and the second toner carrier are arranged. In the case where the toner carrier is disposed to face each other via a liquid developer, a recording medium, or the like, both of them are included. The image forming apparatus according to the present embodiment is configured to be able to apply an electric field between the first toner carrier and the second toner carrier, and electrostatically transfer toner particles between the two. Delivery can be performed.

<Toner carrier>
In the present embodiment, the toner carrying member is a member that adheres and carries toner particles contained in the liquid developer on the surface thereof, and is a member that participates in electrostatic delivery of toner particles. As a method for supporting the toner particles, the toner particles may be supported using electrostatic adhesion force, or may be supported by other physical and chemical adsorption actions. The shape of the toner carrier is not particularly limited, but is preferably a cylindrical shape. In the configuration of a typical image forming apparatus, examples of such a toner carrier include a developer carrier (developing roll), an image carrier (photosensitive drum), and an intermediate transfer member (primary transfer roll). Can be mentioned. In addition, the transfer support member (secondary transfer roll) is equivalent to this from the viewpoint of being a member involved in electrostatic delivery of toner particles.

<Power supply unit>
The image forming apparatus according to the present embodiment includes a power supply device that applies an electric field between the first toner carrier and the second toner carrier. By utilizing this electric field, electrostatic transfer of toner particles is performed between the first toner carrier and the second toner carrier. The method for applying the electric field is not particularly limited. For example, by connecting a power supply device to the first toner carrier and applying a bias voltage, the first toner carrier and the second toner carrier are placed between the first toner carrier and the second toner carrier. An electric field may be applied, or an electric field may be applied between the two toner carriers by connecting a power supply device and applying a bias voltage.

<Resistance layer>
In the present embodiment, the first toner carrier has a resistance layer on the surface thereof. That is, the image forming apparatus according to the present embodiment includes a resistance layer on the surface of at least one of the toner carriers when the toner particles are electrostatically transferred between the two toner carriers. The electrical resistance per unit area of the resistance layer is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. Thereby, the mobility of the toner particles can be limited to a suitable range, and the occurrence of image noise such as granular unevenness can be suppressed.

Here, when the electric resistance per unit area of the resistance layer is less than 10 ⁵ Ω · cm ² , the mobility of the toner particles cannot be sufficiently suppressed, and granular unevenness occurs. On the other hand, if it exceeds 10 ⁸ Ω · cm ² , the toner particles can be moved electrostatically without any problems in the initial stage, but if used continuously, the surface potential of the toner carrier increases (charges up). Discharge occurs irregularly between other toner carriers arranged opposite to each other. Such discharge causes image noise called discharge unevenness. In addition, electrostatic movement of the toner particles may be excessively hindered, and the toner particle delivery efficiency may be reduced. Therefore, the electrical resistance per unit area of the resistance layer needs to be 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. Further, from the viewpoint of more effectively suppressing the occurrence of granular unevenness, the electric resistance per unit area of the resistance layer is more preferably 10 ⁶ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less, and particularly preferably. Is 10 ⁷ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less.

  The toner carrier having a resistance layer on the surface is preferably composed of a conductive base material and a resistance layer provided on the base material. Here, the material of the base material is not particularly limited, and for example, metal materials such as aluminum, stainless steel, and iron, and alloy materials thereof can be used. As the resistance layer, for example, a conductive material in which a conductive filler is dispersed can be used. Examples of the resin material include rubber materials such as silicone rubber, urethane rubber, nitrile rubber, natural rubber and isoprene rubber, foams of thermosetting resins such as polyurethane, epoxy resin and acrylic resin, or heat such as polyethylene and polystyrene. Rubber foam of plastic resin, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate resin, silicone resin And a resin material such as a fluororesin. Examples of the filler used for imparting conductivity to each layer include carbon black such as kettin black, acetylene black, and furnace black, metal powder, metal oxide fine particles, and the like, or a mixture thereof. The resistance value of the resistance layer can be adjusted by the filler content ratio.

  In consideration of the durability at the actual printing site, the toner carrier has a predetermined thickness (specifically, 0.5 μm) so as not to damage the surface of another toner carrier arranged oppositely. It is preferable that an elastic layer (about 30 mm) is included. However, when the elastic layer having such a thickness is used as a resistance layer, and the resistance component is uniformly distributed over the entire resistance layer to achieve the above-described electrical resistance value per unit area as a whole layer, before the nip portion, However, it is possible to avoid charging leakage due to excessive electric field formation and charge-up, but there may be a time delay in development and transfer electric field formation after entering the nip, resulting in a decrease in development and transfer efficiency. is there. In particular, this effect is noticeable during high-speed image formation.

  In order to avoid such a problem, the resistance layer of the toner carrier preferably includes a plurality of layers. That is, the resistance layer is composed of an elastic layer having a relatively low resistance and a surface layer having a relatively high resistance formed thereon. More preferably, it is preferable that the resistance of the toner carrier is substantially defined only by the surface layer having a relatively high resistance. That is, it is preferable that the outermost surface layer of the plurality of layers has the highest electrical resistance. As a result, excessive electric field formation in the space before the nip portion is suppressed to prevent occurrence of granular unevenness, and prompt electric field formation at the nip portion is possible, and electric field formation at the nip portion is insufficient. Image formation can be performed without causing a reduction in development and transfer efficiency.

<Measuring method of electric resistance per unit area of resistance layer>
In this embodiment, the electrical resistance per unit area of the resistance layer provided in the toner carrier is measured by the following method.

First, the toner carrier is brought into contact with a flat metal plate by applying a load of 0.4 N / cm ² to form a nip state between the toner carrier and the metal plate. Next, in this state, a voltage of V = 100 V is applied between the base material (conductive core) of the toner carrier and the metal plate, and current I (unit: A) is measured. Further, the nip area S generated between the toner carrier and the metal plate (contact area between the toner carrier and the metal plate when a load of 0.4 N / cm ² is applied) (unit: cm ² ) is separately provided. taking measurement. Then, the electrical resistance R per unit area of the resistance layer is calculated by the following formula (1).
R = (V / I) × S (1)
R (unit: Ω · cm ² ) calculated by the equation (1) is a resistance value per unit area through the thickness direction. Therefore, it does not depend on the nip area or the thickness of the resistance layer. Since this value correlates with the moving speed of the toner particles, it can be used as an index for measuring the effect of suppressing the mobility of the toner particles in the resistance layer.

  The electrical resistance per unit area of members other than the toner carrier can also be measured according to the same method. For example, when measuring the electrical resistance of paper (recording medium), a conductive sheet (for example, metal me (trade name, manufactured by Toray Film Processing Co., Ltd.)) is wrapped around the toner carrier, and the toner is carried via the paper. By forming a nip state between the body and the metal plate and applying a voltage between the conductive sheet and the metal plate, the electrical resistance per unit area of the paper under the same conditions can be measured.

<Configuration and operation of image forming apparatus>
An example of a specific configuration and operation of the image forming apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is merely an example, and the present invention is not limited to this.

  As shown in FIG. 1, the image forming unit of the image forming apparatus 100 includes a photosensitive drum as the image carrier 1, a charging device 2, an exposure device 3, a developing device 4, an intermediate transfer member 5, a transfer support member 6, and an image carrier. A body cleaning device 7 and an intermediate transfer body cleaning device 8 are provided.

  The image carrier 1 is a cylindrical toner carrier having a photosensitive layer (not shown) formed on the surface thereof, and is driven to rotate in the direction of arrow A in FIG. On the outer periphery of the image carrier 1, a charging device 2, an exposure device 3, a developing device 4, an intermediate transfer member 5, and an image carrier cleaning device 7 are sequentially arranged along the rotation direction of the image carrier 1.

  The charging device 2 charges the surface of the image carrier 1 to a predetermined potential. The exposure apparatus 3 forms an electrostatic latent image by irradiating the surface of the image carrier 1 with light and lowering the charge level in the irradiated area.

  The developing device 4 develops the electrostatic latent image formed on the image carrier 1. That is, the liquid developer is transported to the developing area of the image carrier 1 and toner particles contained in the liquid developer are supplied to the electrostatic latent image on the surface of the image carrier 1 to form a toner image.

<Development process>
Here, the development process will be described. In the image forming apparatus 100, the developer carrier 9 corresponds to a first toner carrier, and the image carrier 1 corresponds to a second toner carrier. The developer carrier 9 as the first toner carrier has a resistance layer on its surface, and the electrical resistance per unit area of the resistance layer is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ^2. It is as follows.

  First, a developing bias voltage is applied to the developer carrier 9 of the developing device 4 from a power supply device (not shown). The toner particles in the liquid developer are electrostatically attracted to the latent image portion of the image carrier 1 according to the electric field generated by the balance with the potential of the electrostatic latent image on the image carrier 1, The latent image is developed.

  The liquid developer 12 is accommodated in a developer tank 13. A part of the pumping member 14 is immersed in the liquid developer 12 and is driven to rotate in the direction of arrow D in FIG. As a result, the liquid developer 12 is pumped up and regulated to a constant film thickness by the regulating blade 15 provided in contact with the pumping member 14. After the liquid developer is regulated, the pumping member 14 contacts the supply member 16 and delivers the liquid developer to the supply member 16. The supply member 16 rotates in the direction of arrow C in FIG. 1 opposite to the rotation direction of the developer carrier 9, and transports the liquid developer delivered in that direction. Thereafter, the liquid developer is transferred onto the developer carrier 9 at the facing portion between the supply member 16 and the developer carrier 9. The liquid developer on the developer carrier 9 is charged by a toner charging device 17 (for example, a corotron charger, a charging roller, etc.) so that the toner particles in the liquid developer are charged. The liquid developer containing the charged toner particles moves to the development nip portion that is the facing portion between the image carrier 1 and the developer carrier 9. Here, the thin layer made of the liquid developer formed on the developer carrier 9 abuts on the image carrier 1 which is a photosensitive member, and develops the electrostatic latent image on the image carrier 1.

  The liquid developer that is not used for development and remains on the developer carrier 9 is collected by the development cleaning member 18. Since the liquid developer recovered by the developer cleaning member 18 is different in solid content concentration (content ratio of toner particles) from the original liquid developer 12, it is recovered in a tank (not shown) separate from the developer tank 13. Then, after the solid content concentration is adjusted, it is supplied to the developer tank 13 again.

  The pumping member 14 may be a urethane or NBR (nitrile butadiene rubber) rubber roller, or an anilox roller having a recess on the surface, and the supply member 16 may be a urethane or NBR rubber roller. it can. The pumping member may also serve as the supply member without providing the supply member. Further, the relative rotation direction between the rollers in the developing device 4 may be different from this.

As described above, the image forming apparatus 100 is disposed with the developer carrier 9 (first toner carrier) and the developer carrier 9 so as to face the developer carrier 9 and develop with the toner particles carried by the developer carrier 9. And an image carrier 1 (second toner carrier) that forms a toner image on the surface, and a power supply device that applies an electric field between the developer carrier 9 and the image carrier 1. The body 9 has a resistance layer on its surface, and the electric resistance per unit area of the resistance layer is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. As a result, even when toner particles having a high average circularity and a high electrostatic moving speed are used, the mobility of the toner particles is limited by the resistance layer provided in the developer carrier 9, and granular unevenness is generated. In addition, electrostatic transfer of toner particles can be performed between the developer carrier 9 and the image carrier 1. Further, since toner particles having a high average circularity can be used, the development efficiency is high.

<Primary transfer process>
Next, the primary transfer process will be described. As shown in FIG. 1, the intermediate transfer unit includes an intermediate transfer member 5, a transfer support member 6, and an intermediate transfer member cleaning device 8. In the image forming apparatus 100, the intermediate transfer member 5 corresponds to a toner carrier (third toner carrier). The intermediate transfer member 5 has a resistance layer on the surface, and the electric resistance per unit area of the resistance layer is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less.

  The intermediate transfer member 5 is disposed to face the image carrier 1 and rotates in the direction of arrow E in FIG. 1 while being in contact with the image carrier 1. Then, primary transfer is performed from the image carrier 1 to the intermediate transfer member 5 at the nip portion between the intermediate transfer member 5 and the image carrier 1.

  In the primary transfer process, a transfer bias voltage is applied to the intermediate transfer member 5 from a power supply device (not shown). As a result, a transfer electric field is formed between the intermediate transfer member 5 and the image carrier 1 in the primary transfer region, and the toner image on the image carrier 1 is electrostatically attracted to the intermediate transfer member 5, whereby the toner image Is transferred to the intermediate transfer member 5.

  When the toner image is transferred to the intermediate transfer member 5, the image carrier cleaning device 7 removes the toner particles remaining on the image carrier 1, and the next image formation is performed. Further, an eraser lamp 10 is installed between the image carrier cleaning device 7 and the charging device 2 as necessary.

As described above, the image forming apparatus 100 is disposed as the third toner carrier facing the image carrier 1, and the intermediate transfer member 5 to which the toner image formed on the surface of the image carrier 1 is transferred. And a power supply device that applies an electric field between the image carrier 1 and the intermediate transfer member 5, and the intermediate transfer member 5 has a resistance layer on the surface thereof, and a unit area per unit area of the resistance layer The electric resistance is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. As a result, even when toner particles having a high average circularity and a high electrostatic moving speed are used, the mobility of the toner particles is limited by the resistance layer provided in the intermediate transfer body 5 without causing granular unevenness. The toner particles can be electrostatically transferred between the image carrier 1 and the intermediate transfer member 5. Further, since toner particles having a high average circularity can be used, transfer efficiency is high.

<Secondary transfer process>
Next, the secondary transfer process will be described. As shown in FIG. 1, the intermediate transfer body 5 and the transfer support member 6 are disposed so as to face each other with the recording medium 11 interposed therebetween, and rotate in contact with each other via the recording medium 11. Then, secondary transfer from the intermediate transfer body 5 to the recording medium 11 is performed at the nip portion between the intermediate transfer body 5 and the transfer support member 6. The recording medium 11 is conveyed along the direction of arrow F in FIG. 1 to the secondary transfer position in synchronization with the secondary transfer timing.

  In the secondary transfer process, a transfer bias voltage is applied to the transfer support member 6 from a power supply device (not shown). As a result, a transfer electric field is formed between the intermediate transfer member 5 and the transfer support member 6, and the recording medium 11 passed between the intermediate transfer member 5 and the transfer support member 6 is transferred onto the intermediate transfer member 5. By electrostatically adsorbing the toner image, the toner image is transferred onto the recording medium 11.

  When the toner image is transferred onto the recording medium 11, the intermediate transfer member cleaning device 8 removes the toner particles remaining on the intermediate transfer member 5, and the next primary transfer is performed.

Here, the transfer support member 6 can also employ a configuration in which a resistance layer is provided on a conductive base material such as a metal material, as in the toner carrier, and the material of the base material and the resistance layer is also the toner. It can be the same as the carrier. In the secondary transfer process, the strength of the transfer electric field is determined by the member having the highest resistance among the intermediate transfer member 5, the transfer support member 6, and the recording medium 11. Therefore, in order to maintain the secondary transfer efficiency high while using toner particles having a high degree of circularity, the electrical resistance per unit area of the resistance layer of the intermediate transfer member 5 and the unit resistance per unit area of the resistance layer of the transfer support member 6 Of the electric resistance and the electric resistance per unit area of the recording medium 11, the largest value is preferably 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. Moreover, in order to implement | achieve such a structure, it is preferable that the member with the highest resistance has a resistance layer among these, and this resistance layer contains several layers. Specifically, the electric resistance of the resistance layer of the intermediate transfer member 5 is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less, and the electric resistance of the resistance layer of the transfer support member 6 and the electric power of the recording medium 11 are recorded. When the resistance is smaller than this value, even if the resistance layer of the transfer assisting member 6 is a single layer, the image density does not decrease. However, when the electrical resistance of the resistance layer of the transfer support member 6 exceeds the electrical resistance of the resistance layer of the intermediate transfer member 5, the resistance layer of the transfer support member 6 preferably includes a plurality of layers. In order to suppress granular unevenness regardless of the recording medium 11, the higher value of the electric resistance of the resistance layer of the intermediate transfer body 5 and the electric resistance of the resistance layer of the transfer support member 6 is 10 ⁵ Ω. · Cm ² or more and 10 ⁸ Ω · cm ² or less is sufficient. Of course, both may be included in the range of 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less.

As described above, the image forming apparatus 100 applies an electric field between the transfer support member 6 disposed opposite to the intermediate transfer body 5 with the recording medium 11 interposed therebetween, and between the intermediate transfer body 5 and the transfer support member 6. The transfer assisting member 6 has a resistance layer on the surface thereof, the electric resistance per unit area of the resistance layer of the intermediate transfer member 5, and the per unit area of the resistance layer of the transfer assisting member 6. Among these, and the electric resistance per unit area of the recording medium 11, the largest value can be 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. As a result, even when toner particles having a high average circularity and a high electrostatic moving speed are used, the mobility of the toner particles is limited, and electrostatic delivery can be performed without causing granular unevenness. it can. Further, since toner particles having a high average circularity can be used, transfer efficiency is high.

Note that the intermediate transfer member may not be provided and the image carrier may be directly transferred to the recording medium. In other words, the image forming apparatus according to the present embodiment includes a transfer support member disposed to face the image carrier with the recording medium interposed therebetween, and a power supply device that applies an electric field between the image carrier and the transfer support member. The transfer assisting member has a resistance layer on its surface, and the larger of the electrical resistance per unit area of the resistance layer and the electrical resistance per unit area of the recording medium is 10 ⁵ Ω · cm. ^The structure may be ² or more and 10 ⁸ Ω · cm ² or less. In this case as well, the above-described effects are similarly shown.

<Fixing process>
After the secondary transfer, the recording medium 11 is conveyed to a fixing device (not shown), where toner particles on the recording medium 11 are heated and melted, and an image is fixed on the recording medium 11.

<Others>
1 illustrates a single-color image forming apparatus having one set of an image carrier and a developing device, but there are four sets of image carriers and developing devices, each of which forms an image of each color of CMYK. Thus, the effect of the present invention can be obtained even in a color image forming apparatus configured to superimpose images of respective colors on the intermediate transfer member. In addition, other conventional process technologies relating to electrophotography can be applied to the image forming apparatus of the present embodiment in combination with an arbitrary configuration according to the purpose of the image forming apparatus.

Hereinafter, the liquid developer used in the image forming apparatus of the present embodiment will be described in detail.
<Liquid developer>
The liquid developer in the present embodiment includes an insulating liquid and toner particles. Such a liquid developer can contain any other additive as long as it contains an insulating liquid and toner particles. Examples of other components include a charge control agent, a thickener, and a toner dispersant.

  Here, the content of the toner particles contained in the liquid developer is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, from the viewpoint of the fixing property of the toner particles and the heat stability of the liquid developer. Yes, more preferably 20 to 40% by mass.

When the content of the toner particles contained in the liquid developer is 50% by mass or less, the viscosity of the liquid developer becomes an appropriate value, which is convenient in manufacturing and handling. The viscosity of the liquid developer is preferably 5 mPa · s or more and 1000 mPa · s or less at 25 ° C. When the viscosity of the liquid developer is 5 mPa · s or more, the mobility of the toner particles tends to be easily suppressed. Further, the viscosity of the liquid developer is under 1000 mPa · s or more, the handling of the liquid developer at the time of or feeding a liquid developer or stirring the liquid developer becomes easy and the uniform liquid developer The burden on each device to obtain is reduced.

  Such a liquid developer is useful as a developer for an electrophotographic image forming apparatus. More specifically, electrophotographic liquid developers, paints, electrostatic recording liquid developers, and ink jet printers used in electrophotographic image forming apparatuses such as copying machines, printers, digital printing machines, and simple printing machines. It can be used as an oil-based ink or an ink for electronic paper.

<Toner particles>
The toner particles in the present embodiment include a resin and a colorant dispersed in the resin. Such toner particles can contain any other component as long as these components are contained. Examples of other components include pigment dispersants, waxes, charge control agents, and the like.

  The toner particles in the present embodiment have an average circularity of 0.90 or more and 0.98 or less. If the average circularity is less than 0.90, the transfer efficiency may decrease due to the distorted particle shape. On the other hand, when the average circularity exceeds 0.98, the mobility of the toner particles becomes remarkably high, and even if the resistance value of the resistance layer provided in the toner carrier is controlled, it is difficult to suppress the mobility. Here, the average circularity is preferably 0.90 or more and 0.96 or less, and more preferably 0.90 or more and 0.94 or less. When the average circularity occupies such a range, occurrence of granular unevenness can be more effectively suppressed.

  Here, the “circularity” indicates a numerical value obtained by dividing the circumference of a circle having an area equal to the area of the two-dimensionally projected particle by the circumference of the particle, and is obtained by calculation by optically detecting the particle. Value. The “average circularity” indicates an arithmetic average value obtained by measuring the circularity of a plurality of particles and obtaining from the obtained circularity group. From the viewpoint of measurement reliability, it is preferable that the average circularity is calculated using the measurement results of 100 or more toner particles.

  In the present embodiment, the median diameter of the toner particles is preferably 0.5 μm or more and 5.0 μm or less. Such a median diameter is smaller than the particle diameter of toner particles of a conventional dry developer, which is one of the features of the present embodiment. However, when the median diameter is less than 0.5 μm, the particles are If the diameter is too small, the mobility in the electric field may be deteriorated and the developability may be deteriorated. If it exceeds 5 μm, the uniformity may be deteriorated and the image quality may be deteriorated. The median diameter here refers to D50. Moreover, a more preferable median diameter is 0.5 μm or more and 2.0 μm or less for the reason described above.

  In the present embodiment, the median diameter and average circularity of toner particles can be determined using a flow type particle image analyzer (trade name: “FPIA-3000S”, manufactured by Sysmex). This apparatus is preferable because the insulating liquid can be used as a dispersion medium as it is, and thus the state of particles in an actual dispersion state can be measured as compared with a system in which measurement is performed in an aqueous system.

<Evaluation method of mobility of toner particles>
As described above, the toner particles in the present exemplary embodiment have a high average circularity and high mobility when performing electrostatic delivery between toner carriers. Here, the mobility of the toner particles in the image forming process can be evaluated as follows.

  First, a sheet having aluminum deposited on one side of a PET (polyethylene terephthalate) sheet is prepared. The sheet is wound around a developer carrier so that the surface on which aluminum is deposited is on the outside, and a thin layer made of a liquid developer is formed thereon, and then brought into contact with the image carrier. As the bias voltage is rotated while the surface potential of the image carrier is set to 0 V, the waveform shown in FIG. 2 is monotonically changed from -400 V to 400 V in proportion to time as a bias voltage. Voltage) is applied, and the current flowing into the surface on which the aluminum is deposited when the voltage is applied is measured.

  FIG. 3 is an example of a measurement result. Between −400 V and 0 V, the toner particles are attracted toward the developing carrier, so that the toner particles do not move, and only a constant charging current accompanying a change in applied voltage is observed. When the applied voltage becomes 0 V or higher, the toner particles gradually start moving toward the image carrier, and the charging current accompanying the movement of the toner particles is added to the constant charging current accompanying the change in the applied voltage. The charging current accompanying the movement of the toner particles is referred to as “moving current”. The moving current changes as follows.

  While the absolute value of the positive applied voltage is small, there are few toner particles that move by the electric field, and the moving current is small. As the applied voltage gradually increases, the moving toner particles increase and the moving current also increases. The moving current reaches a peak at point A in FIG. Thereafter, since the number of toner particles on the developer carrying member decreases, the moving current gradually converges, and finally the moving current does not flow.

  In the present embodiment, the reciprocal of the voltage (point B) when the moving current reaches a peak is used as an index of toner particle mobility. In other words, the higher the mobility of the toner particles, the larger the value of the mobility index because the movement current reaches a peak at a smaller applied voltage. On the other hand, toner particles having low mobility reach a peak at a large applied voltage, and thus the mobility index shows a small value. Thus, the mobility of the toner particles can be evaluated based on the mobility index.

<Method for producing toner particles>
The toner particles in the present embodiment can be manufactured based on a conventionally known technique of granulation. In addition, the granulation method includes suspension polymerization method, emulsion polymerization method, fine particle aggregation method, method of adding a poor solvent to a resin solution to precipitate, spray drying method, etc. There is also a manufacturing method in which the resin composition of the toner particles is made to have a core / shell structure with different resins.

  The method for producing toner particles of the present embodiment is not particularly limited, but in order to obtain toner particles having a small diameter and a sharp particle size distribution, it is preferable to employ a granulation method rather than a pulverization method. This is because highly meltable resins and highly crystalline resins are soft and difficult to grind even at room temperature. According to the granulation method, even such a resin is suitable because a desired particle size can be easily obtained.

  In addition, among the above production methods, the core resin is dissolved in a good solvent to obtain a resin solution, and the resin solution is mixed with an interfacial tension modifier for a poor solvent having a SP value different from that of the good solvent, and sheared. And forming droplets and then volatilizing the good solvent to form resin fine particles. According to this method, the particle size and shape of the toner particles can be controlled to a high degree by appropriately adjusting the shearing method, the interfacial tension difference, or the interfacial tension adjusting agent (shell resin fine particles). Toner particles having a particle size distribution and shape can be obtained.

<Core / shell structure>
The toner particles in the present embodiment preferably have a core / shell structure in which a shell resin is attached or coated on the surface of the core resin. When the toner particles have a core / shell structure, it is easy to control the particle shape (that is, the average circularity) and the particle diameter of the toner particles, and it is possible to realize a low adhesion amount of toner particles and an improvement in transfer efficiency.

  The toner particles having a core / shell structure are as follows. That is, the toner particles (C) are dispersed in the insulating liquid (L), and the toner particles (C) include core particles (A) in which the shell particles (A) containing the shell resin (a) contain the core resin (b). B) has a structure attached or coated on the surface. In the following description, for convenience, the liquid developer containing toner particles (C) having a core / shell structure may be referred to as a liquid developer (X). In addition, toner particles having a core / shell structure may be referred to as core / shell type toner particles.

  The mass ratio [(A) :( B)] of the shell particles (A) and the core particles (B) is preferably 1:99 to 80:20. If the content (mass ratio) of the shell particles (A) is too low, the blocking resistance of the toner particles may be lowered. If the content (mass ratio) of the core particles is too high, the particle size uniformity of the toner particles may decrease.

  From the viewpoint of the fixing property of the toner particles (C) and the heat stability of the liquid developer (X), the content of the toner particles (C) in the liquid developer (X) is preferably 10 to 50% by mass. More preferably, it is 15-45 mass%, More preferably, it is 20-40 mass%.

<Shell resin (a)>
The shell resin of the present embodiment preferably contains a vinyl resin, and the vinyl resin preferably has a long hydrocarbon chain in the side chain. As described above, the shell resin covering the surface of the toner particles has a functional group having a high affinity with the insulating liquid, whereby the dispersibility of the toner particles in the insulating liquid is improved, and the mobility of the toner particles is improved. Variations can be suppressed. As a result, the mobility of the toner particles can be easily controlled by the resistance layer of the toner carrier.

  Here, the “hydrocarbon long chain” is a hydrocarbon group having 8 to 30 carbon atoms. The hydrocarbon group may be a straight chain (for example, an octyl group), or may be branched (also referred to as branched), but in this application, branches and branches may be collectively expressed as “branched”. (For example, an isooctyl group) or a part or all of them may be cyclized. In addition, as long as the hydrocarbon group is composed of carbon and hydrogen with a carbon-carbon bond as the main chain, a part of hydrogen may be substituted with another substituent (for example, halogen). As long as it has a structure, it can have a valence of monovalent (for example, an alkyl group) or divalent or more (for example, an alkylene group) (in addition, when elements other than carbon and hydrogen are included, the mass of other elements is not included) Suppose). In addition, the hydrocarbon group includes a group that is part of a group (for example, an alkoxy group) that is referred to by another name in terms of chemical nomenclature by bonding to other elements other than carbon and hydrogen. In addition, the hydrocarbon group may partially include a double bond in the carbon-carbon bond (for example, an oleyl group).

Examples of such a long hydrocarbon chain include a linear alkyl group or a branched alkyl group represented by the general formula “C _n H _{2n + 1} ” (n is an integer of 8 to 30).

Moreover, it is preferable that a hydrocarbon long chain exists in the side chain of a vinyl resin. This is because the effect is easily exhibited. That is, the shell resin preferably contains a vinyl resin, and the hydrocarbon long chain is preferably present in the side chain of the vinyl resin. Here, the “side chain of the vinyl resin” is a site branched from the main chain of carbon-carbon bonds linked by polymerization of vinyl groups (in other words, a site not included in the main chain). When the resin is an acrylic resin, it refers to an ester group portion of an acrylic ester that is a structural unit of the acrylic resin. The vinyl resin refers to a resin (polymer) obtained by polymerizing a monomer having a polymerizable double bond (vinyl group (CH ₂ ═CH— or vinylidene group CH ₂ ═C =)) including an acrylic resin. .

<Vinyl resin>
The vinyl resin may be a homopolymer obtained by homopolymerizing a monomer having a polymerizable double bond (a homopolymer containing a bond unit derived from a vinyl monomer), or a polymerizable double bond. It may be a copolymer obtained by copolymerizing two or more monomers having a bond (a copolymer containing a bond unit derived from a vinyl monomer). Examples of the monomer having a polymerizable double bond include the following (1) to (9). In addition, when a C8-30 hydrocarbon group is contained among the following, it becomes a hydrocarbon long chain.

(1) Hydrocarbon having a polymerizable double bond The hydrocarbon having a polymerizable double bond is, for example, an aliphatic hydrocarbon having a polymerizable double bond represented by the following (1-1) or the following (1 -2) is preferably an aromatic hydrocarbon having a polymerizable double bond.

(1-1) Aliphatic hydrocarbon having a polymerizable double bond An aliphatic hydrocarbon having a polymerizable double bond is, for example, a chain having a polymerizable double bond represented by the following (1-1-1). It is preferably a hydrocarbon or a cyclic hydrocarbon having a polymerizable double bond represented by the following (1-1-2).

(1-1-1) Chain hydrocarbon having a polymerizable double bond Examples of the chain hydrocarbon having a polymerizable double bond include alkenes having 2 to 30 carbon atoms (for example, ethylene, propylene, butene). , Isobutylene, pentene, heptene, diisobutylene, octene, dodecene or octadecene); alkadienes having 4 to 30 carbon atoms (for example, butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene or 1,7-octadiene) Etc.).

(1-1-2) Cyclic hydrocarbon having a polymerizable double bond Examples of the cyclic hydrocarbon having a polymerizable double bond include mono- or dicycloalkene having 6 to 30 carbon atoms (for example, cyclohexene, vinyl, etc.). Cyclohexene or ethylidenebicycloheptene); mono- or dicycloalkadienes having 5 to 30 carbon atoms (for example, cyclopentadiene or dicyclopentadiene) and the like.

(1-2) Aromatic hydrocarbon having a polymerizable double bond As an aromatic hydrocarbon having a polymerizable double bond, for example, styrene; hydrocarbyl of styrene (for example, alkyl having 1 to 30 carbon atoms) , Cycloalkyl, aralkyl and alkenyl) substituted (eg, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene) Crotylbenzene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, etc.); vinylnaphthalene and the like.

(2) Monomers having a carboxyl group and a polymerizable double bond and salts thereof Examples of the monomer having a carboxyl group and a polymerizable double bond include unsaturated monocarboxylic acids having 3 to 15 carbon atoms. [For example, (meth) acrylic acid, crotonic acid, isocrotonic acid, cinnamic acid, etc.]; unsaturated dicarboxylic acid having 3 to 30 carbon atoms (anhydride) [for example, (anhydrous) maleic acid, fumaric acid, itaconic acid, (Anhydrous) citraconic acid or mesaconic acid, etc.]; monoalkyl (carbon number 1 to 10) ester of unsaturated dicarboxylic acid having 3 to 10 carbon atoms (for example, maleic acid monomethyl ester, maleic acid monodecyl ester, fumaric acid) Monoethyl ester, itaconic acid monobutyl ester, citraconic acid monodecyl ester and the like). In this specification, “(meth) acryl” means at least one of acrylic and methacrylic.

  Examples of the salt of the monomer include alkali metal salts (for example, sodium salt or potassium salt), alkaline earth metal salts (for example, calcium salt or magnesium salt), ammonium salts, amine salts, and 4 Class ammonium salt etc. are mentioned.

  The amine salt is not particularly limited as long as it is an amine compound. For example, primary amine salt (for example, ethylamine salt, butylamine salt or octylamine salt); secondary amine salt (for example, diethylamine salt or dibutylamine salt) ); Tertiary amine salt (for example, triethylamine salt or tributylamine salt) and the like.

  Examples of the quaternary ammonium salt include tetraethylammonium salt, triethyllaurylammonium salt, tetrabutylammonium salt, and tributyllaurylammonium salt.

  Examples of the salt of the monomer having a carboxyl group and a polymerizable double bond include sodium acrylate, sodium methacrylate, monosodium maleate, disodium maleate, potassium acrylate, potassium methacrylate, monopotassium maleate. , Lithium acrylate, cesium acrylate, ammonium acrylate, calcium acrylate, and aluminum acrylate.

(3) Monomers having a sulfo group and a polymerizable double bond and salts thereof (4) Monomers having a phosphono group and a polymerizable double bond and salts thereof (5) Hydroxyl groups and a polymerizable double bond (6) Nitrogen-containing monomer having a polymerizable double bond Examples of the nitrogen-containing monomer having a polymerizable double bond include the following (6-1) to (6-4): The monomer to show is mentioned.

(6-1) Monomer having an amino group and a polymerizable double bond Examples of the monomer having an amino group and a polymerizable double bond include aminoethyl (meth) acrylate and dimethylaminoethyl (meth) acrylate. , Diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, N-aminoethyl (meth) acrylamide, (meth) allylamine, morpholinoethyl (meth) acrylate, 4-vinylpyridine, 2-vinylpyridine, crotylamine N, N-dimethylaminostyrene, methyl-α-acetaminoacrylate, vinylimidazole, N-vinylpyrrole, N-vinylthiopyrrolidone, N-arylphenylenediamine, aminocarbazole, aminothiazole, aminoindole, aminopyrrole, Examples include minoimidazole and aminomercaptothiazole.

  The monomer having an amino group and a polymerizable double bond may be a salt of the monomers listed above. Examples of the salts of the monomers listed above include the salts listed as “Salts of the above monomers” in “(2) Monomers having a carboxyl group and a polymerizable double bond and their salts”. Can be mentioned.

(6-2) Monomer having an amide group and a polymerizable double bond Examples of the monomer having an amide group and a polymerizable double bond include (meth) acrylamide, N-methyl (meth) acrylamide, N -Butyl (meth) acrylamide, diacetone (meth) acrylamide, N-methylol (meth) acrylamide, N, N'-methylene-bis (meth) acrylamide, cinnamic acid amide, N, N-dimethyl (meth) acrylamide, N, N-dibenzyl (meth) acrylamide, (meth) acrylformamide, N-methyl-N-vinylacetamide, N-vinylpyrrolidone and the like can be mentioned.

(6-3) A monomer having 3 to 10 carbon atoms having a nitrile group and a polymerizable double bond As a monomer having 3 to 10 carbon atoms having a nitrile group and a polymerizable double bond, for example, (Meth) acrylonitrile, cyanostyrene, cyanoacrylate, and the like.

(6-4) Monomers having 8 to 12 carbon atoms having a nitro group and a polymerizable double bond As monomers having 8 to 12 carbon atoms having a nitro group and a polymerizable double bond, for example, Nitrostyrene etc. are mentioned.

(7) Monomer having 6 to 18 carbon atoms having an epoxy group and a polymerizable double bond (8) Monomer having 2 to 16 carbon atoms having a halogen element and a polymerizable double bond (9) Polymerization Ester having 4 to 16 carbon atoms having a polymerizable double bond Examples of the ester having 4 to 16 carbon atoms having a polymerizable double bond include vinyl acetate; vinyl propionate; vinyl butyrate; diallyl phthalate; diallyl adipate; Isopropenyl acetate; vinyl methacrylate; methyl-4-vinyl benzoate; cyclohexyl methacrylate; benzyl methacrylate; phenyl (meth) acrylate; vinyl methoxyacetate; vinyl benzoate; ethyl-α-ethoxy acrylate; Alkyl (meth) acrylate [for example, methyl Meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, etc.]; dialkyl fumarate (two alkyl groups have 2 to 8 carbon atoms) A linear alkyl group, a branched alkyl group or an alicyclic alkyl group); a dialkyl maleate (two alkyl groups are a linear alkyl group having 2 to 8 carbon atoms, a branched alkyl group or an alicyclic ring) Poly (meth) allyloxyalkanes (for example, diaryloxyethane, triaryloxyethane, tetraallyloxyethane, tetraallyloxypropane, tetraallyloxybutane, tetrametaallyloxyethane, etc.) ); A monomer having a polyalkylene glycol chain and a polymerizable double bond [for example, poly Ethylene glycol (Mn = 300) mono (meth) acrylate, polypropylene glycol (Mn = 500) mono (meth) acrylate, methyl alcohol ethylene oxide (hereinafter “ethylene oxide” is abbreviated as “EO”) 10 mol adduct (meta ) Acrylate or lauryl alcohol EO 30 mole adduct (meth) acrylate etc.]; poly (meth) acrylates {eg poly (meth) acrylates of polyhydric alcohols [eg ethylene glycol di (meth) acrylate, propylene glycol di ( Meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate or polyethylene glycol di (meth) acrylate]} and the like. In the present specification, “(meth) arylo” means at least one of alilo and metallo.

  Specific examples of the vinyl resin include, for example, a styrene- (meth) acrylic acid ester copolymer, a styrene-butadiene copolymer, a (meth) acrylic acid- (meth) acrylic acid ester copolymer, and a styrene-acrylonitrile copolymer. Copolymers, styrene- (maleic anhydride) copolymers, styrene- (meth) acrylic acid copolymers, styrene- (meth) acrylic acid-divinylbenzene copolymers, and styrene-styrenesulfonic acid- (meth) acrylic acid esters A copolymer etc. are mentioned.

  The vinyl resin may be a homopolymer or copolymer of a monomer having a polymerizable double bond as described in (1) to (9) above, or may be polymerized as described in (1) to (9) above. A polymer obtained by polymerizing a monomer having a double bond and a monomer (m) having a polymerizable double bond having a molecular chain (k) may be used. Examples of the molecular chain (k) include a linear or branched hydrocarbon chain having 12 to 27 carbon atoms, a fluoroalkyl chain having 4 to 20 carbon atoms, and a polydimethylsiloxane chain. The difference in SP value between the molecular chain (k) in the monomer (m) and the insulating liquid (L) is preferably 2 or less. In the present specification, the “SP value” is a method by Fedors [Polym. Eng. Sci. 14 (2) 152, (1974)].

  Although it does not specifically limit as a monomer (m) which has a polymerizable double bond which has a molecular chain (k), For example, the following monomers (m1)-(m3) etc. are mentioned. As the monomer (m), two or more monomers (m1) to (m3) may be used in combination.

Monomer (m1) having a linear hydrocarbon chain having 12 to 27 carbon atoms (preferably 16 to 25 carbon atoms) and a polymerizable double bond
Examples of such a monomer (m1) include mono-linear alkyl of unsaturated monocarboxylic acid (alkyl having 12 to 27 carbon atoms) ester and mono-linear alkyl of unsaturated dicarboxylic acid (alkyl Examples thereof include esters having 12 to 27 carbon atoms. Examples of the unsaturated monocarboxylic acid and unsaturated dicarboxylic acid include (meth) acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid, etc. Examples include a polymer.

  Specific examples of the monomer (m1) include, for example, dodecyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate and ( Examples include (meth) eicosyl acrylate.

Monomer (m2) having a branched hydrocarbon chain having 12 to 27 carbon atoms (preferably 16 to 25 carbon atoms) and a polymerizable double bond
Examples of such a monomer (m2) include a branched alkyl of an unsaturated monocarboxylic acid (alkyl having 12 to 27 carbon atoms) and a monobranched alkyl of an unsaturated dicarboxylic acid (the carbon number of alkyl is 12-27) Ester etc. are mentioned. As said unsaturated monocarboxylic acid and unsaturated dicarboxylic acid, the thing similar to what was enumerated as a specific example of unsaturated monocarboxylic acid and unsaturated dicarboxylic acid in a monomer (m1) is mentioned, for example.

  Specific examples of the monomer (m2) include, for example, 2-decyltetradecyl (meth) acrylate.

  Other examples include a monomer (m3) having a fluoroalkyl chain having 4 to 20 carbon atoms and a polymerizable double bond.

<Melting point>
Melting | fusing point of shell resin (a) becomes like this. Preferably it is 0-220 degreeC, More preferably, it is 30-200 degreeC, More preferably, it is 40-80 degreeC. From the viewpoints of particle size distribution and shape of toner particles, powder flowability of liquid developer (X), heat-resistant storage stability and stress resistance, the melting point of shell resin (a) is the same as that of liquid developer (X). It is preferable that it is more than the temperature at the time of manufacture. If the melting point of the shell resin is lower than the temperature at which the liquid developer is produced, it may be difficult to prevent the toner particles from uniting with each other, and it may be difficult to prevent the toner particles from splitting. . In addition, the distribution width in the particle size distribution of the toner particles is difficult to be narrowed. In other words, there is a possibility that the variation in the particle size of the toner particles becomes large.

  In this specification, the melting point is measured in accordance with a method prescribed in ASTM D3418-82 using a differential scanning calorimeter (“DSC20” or “SSC / 580” manufactured by Seiko Instruments Inc.). It is a thing.

<Mn (number average molecular weight)>
The number average molecular weight (hereinafter also referred to as “Mn”) of the shell resin (a) is preferably 100 to 5000000, preferably 200 to 5000000, and more preferably 500 to 500000. These values were measured using gel permeation chromatography (GPC (Gel Permeation Chromatography), hereinafter abbreviated as “GPC”) described later.

<SP value>
The SP value of the shell resin (a) can be adjusted as appropriate. The SP value of the shell resin (a) is preferably 7 to 18 (cal / cm ³ ) ^1/2 , more preferably 8 to 14 (cal / cm ³ ) ^1/2 .

<Shell particles (A)>
Shell particles (A) in the present embodiment include shell resin (a). Any known method can be adopted as the method for producing the shell particles (A), and the method is not particularly limited. For example, the following methods [1] to [7] can be mentioned [1]: Shell resin (a) is pulverized dry using a known dry pulverizer such as a jet mill [2]. : Disperse the powder of the shell resin (a) in an organic solvent and pulverize it wet using a known wet disperser such as a bead mill or a roll mill [3]: Solution of the shell resin (a) using a spray dryer or the like [4]: Addition or cooling of a poor solvent to the shell resin (a) solution to supersaturate and precipitate the shell resin (a) [5]: Shell resin (a) [6]: The shell resin (a) precursor is polymerized in water by an emulsion polymerization method, a soap-free emulsion polymerization method, a seed polymerization method, a suspension polymerization method, or the like. [7]: Shell resin A precursor of a) is polymerized by dispersion polymerization or the like in an organic solvent.

  Of these methods, the methods [4], [6] and [7] are preferable from the viewpoint of ease of production of the shell particles (A), and more preferably the methods [6] and [7]. Is preferred.

<Volume average particle diameter>
In this case, the volume average particle diameter of the shell particles (A) can be appropriately adjusted so as to be a particle diameter suitable for obtaining toner particles (C) having a desired particle diameter. The volume average particle diameter of the shell particles (A) is preferably 0.0005 to 3 μm. The upper limit of the volume average particle diameter of the shell particles (A) is more preferably 2 μm, and even more preferably 1 μm. The lower limit of the volume average particle diameter of the shell particles (A) is more preferably 0.01 μm, still more preferably 0.02 μm, and most preferably 0.04 μm. For example, when it is desired to obtain toner particles (C) having a volume average particle diameter of 1 μm, the volume average particle diameter of the shell particles (A) is preferably 0.0005 to 0.3 μm, more preferably 0.001. ~ 0.2 μm. For example, when it is desired to obtain toner particles (C) having a volume average particle size of 10 μm, the volume average particle size of the shell particles (A) is preferably 0.005 to 3 μm, more preferably 0.05 to 2 μm. It is.

<Core resin (b) and core particle (B)>
In the present embodiment, the core particle (B) contains the core resin (b). Here, the core resin (b) is preferably a polyester resin.

<Polyester resin>
Examples of the polyester resin include a polycondensate of a polyol and a polycarboxylic acid, a polycarboxylic acid anhydride or a lower alkyl (alkyl group having 1 to 4 carbon atoms) ester of the polycarboxylic acid. A known polycondensation catalyst or the like can be used for the polycondensation reaction.

  The ratio of polyol and polycarboxylic acid is not particularly limited. The equivalent ratio of hydroxyl group [OH] to carboxyl group [COOH] ([OH] / [COOH]) is preferably 2/1 to 1/5, more preferably 1.5 / 1 to 1/4. The ratio between the polyol and the polycarboxylic acid may be set so that the ratio is more preferably 1.3 / 1 to 1/3. Hereinafter, the monomer which comprises a polyester resin is demonstrated.

  Examples of the diol include alkylene glycols having 2 to 30 carbon atoms (for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, octane). Diol, decanediol, dodecanediol, tetradecanediol, neopentyl glycol or 2,2-diethyl-1,3-propanediol, etc .; alkylene ether glycols with Mn = 106 to 10,000 (for example, diethylene glycol, triethylene glycol, dipropylene glycol) Polyethylene glycol, polypropylene glycol or polytetramethylene ether glycol); alicyclic diols having 6 to 24 carbon atoms (for example, 1,4-cyclohexanedimethanol) Is a hydrogenated bisphenol A or the like); an alkylene oxide (hereinafter, “alkylene oxide” is abbreviated as “AO”) adduct of the above alicyclic diol having Mn = 100 to 10,000 (addition mole number is 2 to 100) (for example, 1 , 4-cyclohexanedimethanol EO 10 mol adduct, etc.); bisphenols having 15 to 30 carbon atoms (for example, bisphenol A, bisphenol F or bisphenol S) AO [for example, EO, propylene oxide (hereinafter abbreviated as “PO”) Or butylene oxide, etc.] The above-mentioned AO adduct (eg, EO2-4 of bisphenol A) of an adduct (addition mole number is 2-100) or a polyphenol having 12-24 carbons (eg, catechol, hydroquinone, resorcinol, etc.) Mole adduct or bis Enol A PO 2-4 mol adduct, etc.); weight average molecular weight (hereinafter abbreviated as “Mw”) = 100-5000 polylactone diol (eg, poly-ε-caprolactone diol, etc.); Mw 1000-20,000 polybutadiene Diol etc. are mentioned.

  Examples of the polyol include aliphatic polyhydric alcohols having a valence of 3 to 8 or more and a carbon number of 3 to 10 (for example, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitan, or sorbitol). Etc.); AO (2 to 4 carbon atoms) adduct of trisphenol having 25 to 50 carbon atoms (addition mole number is 2 to 100) (for example, 2 to 4 mol adduct of trisphenol EO or trisphenol polyamide PO2 4 mol adduct, etc.); n = 3-50 novolak resin (for example, phenol novolak or cresol novolak, etc.) AO (carbon number 2-4) adduct (added mole number 2-100) (for example, phenol novolak) PO2 mol adduct or phenol novolac EO4 mol adduct) AO (carbon number 2 to 4) adduct (addition mole number 2 to 100) of polyphenols having 6 to 30 carbon atoms (such as pyrogallol, phloroglucinol or 1,2,4-benzenetriol) (for example, Pyrogallol EO 4 mol adduct, etc.); n = 20-2000 acrylic polyol {for example, monomer having hydroxyethyl (meth) acrylate and other polymerizable double bond [for example, styrene, (meth) acrylic acid or ( And the like) and the like.

  Of these, preferred as polyols are aliphatic polyhydric alcohols and AO adducts of novolak resins, and more preferred are AO adducts of novolak resins.

  Examples of the dicarboxylic acid include alkane dicarboxylic acids having 4 to 32 carbon atoms (for example, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid or octadecanedicarboxylic acid); alkene having 4 to 32 carbon atoms Dicarboxylic acids (eg maleic acid, fumaric acid, citraconic acid or mesaconic acid); branched alkene dicarboxylic acids having 8 to 40 carbon atoms [eg dimer acid or alkenyl succinic acid (eg dodecenyl succinic acid, pentadecenyl) Succinic acid or octadecenyl succinic acid etc.]]; branched alkanedicarboxylic acid having 12 to 40 carbon atoms [eg alkyl succinic acid (eg decyl succinic acid, dodecyl succinic acid or octadecyl succinic acid etc.) etc.]; carbon 8-20 aromatic dicarboxylic acids ( For example, phthalic acid, isophthalic acid, terephthalic acid or naphthalene dicarboxylic acid, etc.) and the like.

<Crystalline / Amorphous>
In the present embodiment, the core resin (b) preferably exhibits crystallinity. Thereby, it is possible to provide an image forming apparatus excellent in low-temperature fixability of the liquid developer. In order to obtain a polyester resin exhibiting crystallinity, the acid and alcohol monomers constituting the polyester resin are preferably composed mainly of aliphatic monomers. The “main component” as used herein indicates that the proportion of the aliphatic monomer is 80% by mass or more with respect to all the structural units in the polyester component.

  Here, “crystallinity” in this specification refers to the ratio (Tm) between the softening point of the resin (hereinafter abbreviated as “Tm”) and the maximum melting temperature of the resin (hereinafter abbreviated as “Ta”). / Ta) is 0.8 or more and 1.55 or less, and the result obtained by differential scanning calorimetry (DSC) is not a stepwise endothermic change but a clear result. It means having an endothermic peak. “Non-crystalline” means that the ratio of Tm to Ta (Tm / Ta) is greater than 1.55. Tm and Ta can be measured by the following method.

<Tm measurement method>
Tm can be measured using a Koka type flow tester (for example, “CFT-500D” manufactured by Shimadzu Corporation). Specifically, while a 1 g measurement sample is heated at a heating rate of 6 ° C./min, a load of 1.96 MPa is applied to the measurement sample by a plunger, and the measurement sample is pushed out from a nozzle having a diameter of 1 mm and a length of 1 mm. . Then, the relationship between “plunger descent amount (flow value)” and “temperature” is drawn on a graph. The temperature at which the plunger descending amount is ½ of the maximum value of the descending amount is read from the graph, and this value (temperature when half of the measurement sample is pushed out of the nozzle) is defined as Tm.

  In the present embodiment, Tm is preferably 40 ° C. or higher, and preferably 80 ° C. or lower from the viewpoint of low-temperature fixability.

<Ta measurement method>
Ta can be measured using a differential scanning calorimeter (for example, “DSC210” manufactured by Seiko Instruments Inc.). Specifically, first, a sample used for measuring Ta is pretreated. After the sample is melted at 130 ° C., the temperature is lowered from 130 ° C. to 70 ° C. at a rate of 1.0 ° C./minute, and then the temperature is lowered from 70 ° C. to 10 ° C. at a rate of 0.5 ° C./minute. Next, the sample is heated at a heating rate of 20 ° C./min by DSC method to measure the endothermic change of the sample, and the relationship between the “endothermic amount” and “temperature” is plotted on a graph. At this time, the temperature of the endothermic peak observed at 20 to 100 ° C. is Ta ′. When there are a plurality of endothermic peaks, the peak temperature with the largest endothermic amount is Ta ′. Then, the sample is stored at (Ta′−10) ° C. for 6 hours, and then stored at (Ta′−15) ° C. for 6 hours. Next, by the DSC method, the sample subjected to the pretreatment was cooled to 0 ° C. at a temperature decrease rate of 10 ° C./min, and then the temperature was increased at a temperature increase rate of 20 ° C./min to measure the endothermic change. The relationship between the "heat absorption and heat generation" and "temperature" is plotted on a graph. The temperature at which the endotherm takes the maximum value is taken as the maximum peak temperature (Ta) of heat of fusion.

<Urethane modified polyester resin>
In the present embodiment, the core resin (b) is more preferably a urethane-modified polyester resin. Here, the “urethane-modified polyester resin” is a resin having a structure in which the end of the polyester is chain-chained with a urethane bond. That is, the urethane-modified polyester resin is a resin in which two or more polyester components are bonded by a structural unit derived from a compound having an isocyanate group. By using such a urethane-modified polyester resin as the core resin (b), there is a tendency that toner particles having an average circularity in the range of 0.90 to 0.96 are easily obtained. Although the details of the reason are unclear, the present inventors have investigated the shape of the toner particles in detail. As a result, the surface of the toner particles having a urethane-modified polyester resin as a core resin has more concave portions than other resins. Therefore, it is presumed that the average circularity is easily obtained as a result of the removal of the solvent when the solvent is removed after the particles are formed, unlike other resins.

  Further, by using the crystalline polyester as described above as the polyester component, the liquid developer can be excellent in low-temperature fixability. Furthermore, the urethane-modified polyester resin has the advantage that elasticity at high temperatures is easily maintained and the offset resistance is excellent. Hereinafter, suitable examples of the monomer constituting the urethane-modified crystalline polyester resin will be described.

  The urethane-modified polyester resin of the present embodiment is obtained by first polymerizing a polyester resin (sometimes referred to as “polyester component”) as a skeleton, and chain-extending the terminal of the polyester resin with di (tri) isocyanate. can get. The di (tri) isocyanate means at least one of diisocyanate and triisocyanate.

  Preferred examples of the aliphatic dicarboxylic acid that is a starting material for the polyester resin include alkane dicarboxylic acids having 4 to 20 carbon atoms, alkene dicarboxylic acids having 4 to 36 carbon atoms, and ester-forming derivatives thereof. . More preferable aliphatic dicarboxylic acids are succinic acid, adipic acid, sebacic acid, maleic acid, fumaric acid, and the like, or ester-forming derivatives thereof.

  Further, preferred as the aliphatic diol which is a starting material of the polyester resin is ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol, or 1 , 10-decanediol and the like.

  Next, a compound having an isocyanate group for forming a urethane-modified polyester resin by bonding and linking polyester resins obtained by polymerizing the above dicarboxylic acid monomer and diol monomer will be described.

  As the compound having an isocyanate group of the present embodiment, a compound having a plurality of isocyanate groups in the molecule is preferable. Examples of such compounds include chain aliphatic polyisocyanates and cyclic aliphatic polyisocyanates.

  Examples of chain aliphatic polyisocyanates include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (hereinafter abbreviated as “HDI”), dodecamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2, and the like. 4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylcaproate, bis (2-isocyanatoethyl) fumarate, bis (2-isocyanatoethyl) carbonate, and 2-isocyanatoethyl-2, Examples include 6-diisocyanatohexanoate, or a combination of two or more of these.

  Examples of the cycloaliphatic polyisocyanate include isophorone diisocyanate (hereinafter abbreviated as “IPDI”), dicyclohexylmethane-4,4′-diisocyanate (hereinafter also referred to as “hydrogenated MDI”), cyclohexylene diisocyanate, methylcyclohexyl. Silylene diisocyanate (hereinafter also referred to as “hydrogenated TDI”), bis (2-isocyanatoethyl) -4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate, Or these 2 or more types combined use etc. are mentioned.

<Number average molecular weight (Mn)>
In the present embodiment, the Mn of the urethane-modified polyester resin is preferably 10,000 or more and 50,000 or less. When Mn is less than 10,000, the resin becomes excessively soft, and offset tends to occur during fixing. On the other hand, if Mn exceeds 50000, the resin is difficult to melt, and the fixing strength tends to decrease. A more preferable range of Mn is 10,000 to 30,000.
<Method of measuring number average molecular weight (Mn) and weight average molecular weight (Mw)>
In the present specification, Mn and Mw of resins (excluding polyurethane resins) are measured for the soluble content of tetrahydrofuran (hereinafter abbreviated as “THF”) using GPC under the following conditions. In addition, Mn and Mw of the urethane-modified polyester resin are those measured by this method Measuring apparatus: “HLC-8120” manufactured by Tosoh Corporation
Column: “TSKgelGMHXL” (2) manufactured by Tosoh Corporation and “TSKgelMultiporeHXL-M” (1) manufactured by Tosoh Corporation
Sample solution: 0.25 mass% THF solution Injection amount of sample solution to the column: 100 μl
Flow rate: 1 ml / min Measurement temperature: 40 ° C
Detector: Refractive index detector Reference material: 12 standard polystyrene (TSK standard POLYSTYRENE) manufactured by Tosoh Corporation (Molecular weight: 500, 1050, 2800, 5970, 9100, 18100, 37900, 96400, 190000, 355000, 1090000, 2890000).

Moreover, in this specification, Mn and Mw of the polyurethane resin are measured under the following conditions using GPC. Measuring device: “HLC-8220GPC” manufactured by Tosoh Corporation
Column: “TSK guardcolumn α” (1) manufactured by Tosoh Corporation and “TSKgel α-M” (1) manufactured by Tosoh Corporation
Sample solution: 0.125 mass% dimethylformamide solution Injection amount of dimethylformamide solution to the column: 100 μl
Flow rate: 1 ml / min Measurement temperature: 40 ° C
Detector: Refractive index detector Reference material: 12 standard polystyrene (TSK standard POLYSTYRENE) manufactured by Tosoh Corporation (Molecular weight: 500, 1050, 2800, 5970, 9100, 18100, 37900, 96400, 190000, 355000, 1090000, 2890000).

<Urethane group concentration>
In this Embodiment, it is preferable that the urethane group density | concentration of urethane-modified polyester resin is 0.5 to 5 mass%. Here, the “urethane group concentration (% by mass)” means a value obtained by multiplying the value obtained by dividing the mass of the urethane group contained in the resin by the mass of the resin by 100. If the urethane group concentration is less than 0.5% by mass, elasticity at a high temperature may not be maintained. If the urethane group concentration exceeds 5% by mass, Tm may be lowered and document offset may be affected.

  Such a urethane group concentration can be measured by the following method, for example. That is, after the urethane-modified polyester resin is thermally decomposed, the generated gas component is analyzed using a gas chromatograph mass spectrometer (GCMS). And the urethane group density | concentration in urethane-modified polyester resin is computed from the ratio of the detected ionic strength. Specific measurement conditions are shown below.

<Pyrolysis conditions>
Measuring device: “PY-2020iD” manufactured by Frontier Laboratories
Mass of measurement: 0.1 mg
Heating temperature: 550 ° C
Heating time: 0.5 minutes.

<GCMS measurement conditions>
Measuring device: “QP2010” manufactured by Shimadzu Corporation
Column: “UltraALLOY-5” manufactured by Frontier Laboratories (inner diameter: 0.25 mm, length: 30 m, thickness: 0.25 μm)
Temperature range: 100 ° C to 320 ° C (held at 320 ° C)
Temperature increase rate: 20 ° C./min.

  The above Mn and urethane group concentrations are, for example, equivalent ratios of the acid group amount of the polycarboxylic acid component and the hydroxyl group amount of the polyol component ([acid Group] / [hydroxyl group]) and the equivalent ratio ([isocyanate group] / [hydroxyl group]) of the isocyanate group amount of the compound having an isocyanate group for bonding the polyester resins to the hydroxyl group amount of the polyester resin. By doing so, it can be controlled within a desired range.

<SP value>
The SP value of the core resin (b) may be adjusted as appropriate. The SP value of the core resin (b) is preferably 8 to 16 (cal / cm ³ ) ^1/2 , more preferably 9 to 14 (cal / cm ³ ) ^1/2 .

<Additives>
The toner particles (C) in the present embodiment preferably contain a colorant in at least one of the shell particles (A) and the core particles (B), and additives other than the colorant (for example, a pigment dispersant, Wax, charge control agent, filler, antistatic agent, mold release agent, ultraviolet absorber, antioxidant, antiblocking agent, heat stabilizer, flame retardant, etc.).

<Colorant>
The colorant contained in the toner particles of the present embodiment is dispersed in the resin. The volume average particle size of such a colorant is preferably 0.3 μm or less. If the volume average particle size of the colorant exceeds 0.3 μm, dispersion may be deteriorated, resulting in a decrease in glossiness and the inability to achieve a desired color.

  As such a colorant, conventionally known pigments and the like can be used without any particular limitation, but from the viewpoint of cost, light resistance, colorability, and the like, for example, the following pigments are preferably used. In terms of color composition, these pigments are usually classified as black pigments, yellow pigments, magenta pigments, and cyan pigments. Basically, colors other than black (color images) are subtractive color mixtures of yellow pigments, magenta pigments, and cyan pigments. Is toned.

  Examples of the pigment (black pigment) contained in the black colorant include carbon black such as furnace black, channel black, acetylene black, thermal black, and lamp black, carbon black derived from biomass, and magnetite, Magnetic powder such as ferrite is also used. Further, nigrosine, which is an azine compound which is a purple black dye, can be used alone or in combination. Nigrosine includes C.I. I. Solvent Black 7 or C.I. I. Selected from Solvent Black 5, etc.

  Examples of the pigment (magenta pigment) contained in the magenta colorant include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the pigment (yellow pigment) contained in the yellow colorant include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, C.I. I. And CI Pigment Yellow 185.

  Examples of the pigment (cyan pigment) contained in the cyan colorant include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment blue 62, C.I. I. Pigment blue 66, C.I. I. And CI Pigment Green 7.

  These colorants can be used alone or in combination of two or more as required.

<Pigment dispersant>
The pigment dispersant has a function of uniformly dispersing the colorant (pigment) in the toner particles, and it is preferable to use a basic dispersant. Here, the basic dispersant is defined as follows. That is, 0.5 g of pigment dispersant and 20 ml of distilled water are placed in a glass screw tube, shaken for 30 minutes using a paint shaker, and then filtered, and the pH of the filtrate obtained is filtered with a pH meter (product) Name: “D-51” (manufactured by HORIBA, Ltd.) and the case where the pH is higher than 7 is defined as a basic dispersant. In addition, when the pH is smaller than 7, it shall call an acidic dispersing agent.

  The kind of such basic dispersant is not particularly limited. For example, an amine group, amino group, amide group, pyrrolidone group, imine group, imino group, urethane group, quaternary ammonium group, ammonium group, pyridino group, pyridium group, imidazolino group, and imidazolium group in the molecule of the dispersant And compounds having a functional group such as (dispersing agent). The dispersant usually corresponds to a so-called surfactant having a hydrophilic part and a hydrophobic part in the molecule, but as long as it has an action of dispersing a colorant (pigment) as described above, Compounds can be used.

  Commercially available products of such basic dispersants include, for example, “Ajisper PB-821” (trade name), “Azisper PB-822” (trade name), “Azisper PB-881” (product) manufactured by Ajinomoto Fine Techno Co., Ltd. Name) or “Solspers 28000” (product name), “Solspurs 32000” (product name), “Solspurs 32500” (product name), “Solspurs 35100” (product name), “Solspurs 37500” (product name) Product name).

  Further, it is more preferable to select a pigment dispersant that does not dissolve in the insulating liquid (carrier liquid). For that reason, “Ajisper PB-821” (trade name), “Ajisper PB-822” (trade name), and “Ajisper PB-881” (trade name) manufactured by Ajinomoto Fine Techno Co. are more preferred. Although the detailed mechanism is unknown, the use of such a pigment dispersant makes it easy to obtain a desired shape.

  The pigment dispersant is preferably added in an amount of 1 to 100% by mass with respect to the colorant (pigment). More preferably, it is 1-40 mass%. If it is less than 1% by mass, the dispersibility of the colorant (pigment) may be insufficient, the required ID (image density) may not be achieved, and the fixing strength may be reduced. On the other hand, when the amount exceeds 100% by mass, a dispersant more than the amount necessary for pigment dispersion is added, and the excess dispersant may be dissolved in the insulating liquid, which may increase the chargeability and fixing strength of the toner particles. May have adverse effects.

  Such pigment dispersants can be used singly or in combination of two or more.

<Insulating liquid>
The insulating liquid contained in the liquid developer of the present embodiment may have a resistance value (approximately 10 ¹¹ to 10 ¹⁶ Ω · cm) that does not disturb the electrostatic latent image. Furthermore, a solvent having low odor and toxicity is preferred. In general, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes and the like can be mentioned. In particular, a normal paraffin solvent and an isoparaffin solvent are preferable in terms of odor, harmlessness, and cost. Specifically, Moresco White (trade name, manufactured by Matsumura Oil Research Co., Ltd.), Isopar (trade name, manufactured by ExxonMobil), Shellsol (trade name, manufactured by Shell Chemicals Japan Co., Ltd.), IP Solvent 1620, IP solvent 2028, IP solvent 2835 (both are trade names, manufactured by Idemitsu Kosan Co., Ltd.), and the like. In consideration of the final fixing step, a solvent having a lower viscosity than that of Moresco P120 (trade name, manufactured by Matsumura Oil Research Co., Ltd.) is more preferable.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Production Example 1> [Production of dispersion (W1) of shell particles (A1)]
In a beaker made of glass, 100 parts by mass of 2-decyltetradecyl methacrylate, 30 parts by mass of methacrylic acid, 70 parts by mass of an equimolar reaction product of hydroxyethyl methacrylate and phenyl isocyanate, and azobismethoxydimethylvaleronitrile 0.5 A part by mass was added and mixed by stirring at 20 ° C. Thereby, a monomer solution was obtained.

  Next, a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, a dropping funnel, a solvent removal device, and a nitrogen introduction tube was prepared. 195 parts by mass of THF was put into the reaction vessel, and the monomer solution was put into a dropping funnel provided in the reaction vessel. After the gas phase portion of the reaction vessel was replaced with nitrogen, the monomer solution was added dropwise to THF in the reaction vessel over 1 hour at 70 ° C. in a sealed state. Three hours after the completion of the dropwise addition of the monomer solution, a mixture of 0.05 parts by mass of azobismethoxydimethylvaleronitrile and 5 parts by mass of THF was placed in a reaction vessel, reacted at 70 ° C. for 3 hours, and then cooled to room temperature. . Thereby, a copolymer solution was obtained.

  Next, 400 parts by mass of the obtained copolymer solution was added dropwise to 600 parts by mass of IP solvent 2028 (made by Idemitsu Kosan Co., Ltd.) with stirring, and then THF was distilled off at 40 ° C. under a reduced pressure of 0.039 MPa. Thereby, a dispersion liquid (W1) of shell particles (A1) was obtained. When the volume average particle diameter of the shell particles (A1) in the dispersion liquid (W1) was measured using a laser type particle size distribution analyzer (trade name: “LA-920”, manufactured by Horiba, Ltd.), the volume average particle diameter was measured. The particle size was 0.12 μm. In this shell particle (A1), the “2-decyltetradecyl” portion in 2-decyltetradecyl methacrylate corresponds to a long hydrocarbon chain.

<Production Example 2> [Production of core resin (b1) forming solution (Y1)]
937 masses of polyester resin (Mn: 6000) obtained from sebacic acid, adipic acid and ethylene glycol (molar ratio 0.8: 0.2: 1) in a reaction vessel equipped with a stirrer, a heating / cooling device and a thermometer And 300 parts by mass of acetone were added and stirred to dissolve uniformly. 63 parts by mass of IPDI was added to this solution and reacted at 80 ° C. for 6 hours. When the NCO value became 0, 28 parts by mass of phthalic anhydride was added and reacted at 180 ° C. for 1 hour to obtain a core resin (b1) which is a crystalline urethane-modified polyester resin. Next, 800 parts by mass of the core resin (b1) and 1200 parts by mass of acetone were placed in a beaker and stirred to uniformly dissolve the core resin (b1) in acetone. As a result, a solution (Y1) for forming the core resin (b1) was obtained. It was 25000 when Mn of core resin (b1) was measured according to the above-mentioned method. Moreover, it was 1.44% when the urethane group density | concentration of core resin (b1) was measured according to the above-mentioned method.

<Production Example 3> [Production of Core Resin (b2) Formation Solution (Y2)]
In a reaction vessel equipped with a stirrer, a heating / cooling device, and a thermometer, an amorphous polyester resin (Mn: 2500) obtained from propion oxide 2-mol adduct of bisphenol A and terephthalic acid (molar ratio 1: 1). 800 parts by mass of the core resin (b2) and 1200 parts by mass of acetone were added and stirred to uniformly dissolve the core resin (b2) in acetone. Thereby, a solution (Y2) for forming the core resin (b2) was obtained.

<Production Example 4> [Production of Colorant Dispersion Liquid (P1)]
In a beaker, 20 parts by mass of acid-treated copper phthalocyanine (trade name: “Fastogen Blue FDB-14”, manufactured by DIC) as a cyan colorant, a pigment dispersant (trade name: “Azisper PB-821”, Ajinomoto Fine Techno ( Co., Ltd.) and 5 parts by mass of acetone and 75 parts by mass of acetone were added, stirred and uniformly dispersed, and then copper phthalocyanine was finely dispersed by a bead mill to obtain a colorant dispersion (P1). The volume average particle diameter of copper phthalocyanine in the colorant dispersion (P1) was 0.2 μm.

<Production Example 5> [Production of liquid developer (Z-1)]
100 parts by mass of the core resin (b2) and 15 parts by mass of copper phthalocyanine (trade name: “Fastogen Blue GNPT”, manufactured by DIC) are sufficiently mixed with a Henschel mixer, and then rotated in the same direction at a heating temperature of 100 ° C. in the same direction. The resulting mixture was cooled and kneaded using a machine, and the resulting mixture was cooled and then coarsely pulverized with a jet pulverizer to obtain a coarsely pulverized toner (D50: 3.0 μm).

  Next, 30 parts by mass of the coarsely pulverized toner, 70 parts by mass of an insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.), and a pigment dispersant (trade name: “V220”, manufactured by ISP Japan) 1 part by mass and 100 parts by mass of zirconia beads were mixed and stirred and mixed by a sand mill for 144 hours. Thereby, a liquid developer (Z-1) was obtained. The toner particles contained in the liquid developer correspond to pulverized toner particles.

<Production Example 6> [Production of liquid developer (Z-2)]
Into a beaker, 40 parts by mass of the core resin (b1) forming solution (Y1) and 20 parts by mass of the colorant dispersion (P1) were added, and 8000 rpm at 25 ° C. using a TK auto homomixer (manufactured by Primics Co., Ltd.). Was stirred and uniformly dispersed to obtain a resin solution (Y1P1).

  Into another beaker, 67 parts by mass of an insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.) and 10 parts by mass of the dispersion liquid (W1) of shell particles (A1) were added and uniformly dispersed. Next, while stirring at 5000 rpm using a TK auto homomixer at 25 ° C., 60 parts by mass of the resin solution (Y1P1) was added and stirred for 2 minutes. Next, this mixed solution was put into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a solvent removal device. After the temperature was raised to 35 ° C., the acetone concentration was reduced to 0.039 MPa at a reduced pressure of 0.039 MPa. Acetone was distilled off from the resin solution (Y1P1) until the content became 5% by mass or less. Thereby, a liquid developer (Z-2) was obtained. The toner particles contained in the liquid developer correspond to core / shell type toner particles.

<Production Example 7> [Production of liquid developer (Z-3)]
Into a beaker, 40 parts by mass of the core resin (b1) forming solution (Y1) and 20 parts by mass of the colorant dispersion (P1) were added, and 8000 rpm at 25 ° C. using a TK auto homomixer (manufactured by Primics Co., Ltd.). Was stirred and uniformly dispersed to obtain a resin solution (Y1P1).

  In another beaker, 67 parts by mass of an insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.) and 13 parts by mass of the dispersion liquid (W1) of shell particles (A1) were charged and uniformly dispersed. Next, while stirring at 10000 rpm using a TK auto homomixer at 25 ° C., 60 parts by mass of the resin solution (Y1P1) was added and stirred for 2 minutes. Next, this mixed solution was put into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a solvent removal device. After the temperature was raised to 35 ° C., the acetone concentration was reduced to 0.039 MPa at a reduced pressure of 0.039 MPa. Acetone was distilled off from the resin solution (Y1P1) until the content became 5% by mass or less. Thereby, a liquid developer (Z-3) was obtained. The toner particles contained in the liquid developer correspond to core / shell type toner particles.

<Production Example 8> [Production of liquid developer (Z-4)]
Into a beaker, 40 parts by mass of the core resin (b2) forming solution (Y2) and 20 parts by mass of the colorant dispersion (P1) were added, and 8000 rpm at 25 ° C. using a TK auto homomixer (manufactured by Primics Co., Ltd.). Was stirred and dispersed uniformly to obtain a resin solution (Y2P1).

  In another beaker, 67 parts by mass of an insulating liquid (trade name: “IP Solvent 2028”, manufactured by Idemitsu Kosan Co., Ltd.) and 13 parts by mass of the dispersion liquid (W1) of shell particles (A1) were charged and uniformly dispersed. Next, while stirring at 10000 rpm using a TK auto homomixer at 25 ° C., 60 parts by mass of the resin solution (Y2P1) was added and stirred for 2 minutes. Next, this mixed solution was put into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a solvent removal device. After the temperature was raised to 35 ° C., the acetone concentration was reduced to 0.039 MPa at a reduced pressure of 0.039 MPa. Acetone was distilled off from the resin solution (Y2P1) until it became 5 mass% or less. Thereby, a liquid developer (Z-4) was obtained. The toner particles contained in the liquid developer correspond to core / shell type toner particles.

<Measurement of median diameter and average circularity>
The median diameter and average circularity of the toner particles contained in each liquid developer obtained as described above were measured using a flow particle image analyzer (trade name: “FPIA-3000S”, manufactured by Sysmex). The same IP solvent 2028 as the insulating liquid of each liquid developer was used as the flow solvent.

  Suspensions were prepared by adding 50 mg of each liquid developer into 20 g of IP solvent 2028 to which 30 mg of a dispersant (trade name: “S13940”, manufactured by Nippon Lubrizol Co., Ltd.) was added. Dispersion treatment was performed for about 5 minutes using a sonic disperser (trade name: “Ultrasonic Cleaner Model VS-150”, manufactured by Welbo Clear).

  Thereafter, using this suspension, the median diameter and average circularity (average value of circularity) of the volume distribution of the toner particles were measured by the above flow particle image analyzer. The results are shown in Table 1.

<Evaluation of mobility of toner particles>
An index of the mobility of toner particles contained in each liquid developer was calculated according to the method described above. The results are shown in Table 1.

<Development and transfer test>
Using the liquid developers (Z-1) to (Z-4) obtained as described above, the developing unit and the primary transfer unit to the secondary transfer unit are respectively separated from the image forming apparatus shown in FIG. A test apparatus that can be extracted and configured to operate individually was configured, and toner particle development and transfer tests were performed using the test apparatus. In the transfer test at the primary transfer portion to the secondary transfer portion, a developer layer was uniformly formed on the photoreceptor (image carrier) using a bar coater, and electrostatic transfer was performed.

  Then, as shown in Tables 2 to 4, while changing the configuration of the resistance layer of the developer carrier, the intermediate transfer member, and the transfer support member, the toner particles are transferred electrostatically, and discharge unevenness, granular unevenness and The state of occurrence of a decrease in image density was evaluated. In addition, electrostatic delivery efficiency (development efficiency and transfer efficiency) was measured.

<Resistance layer>
In Examples 1 to 8 and Comparative Examples 1 to 15, the electric resistance per unit area is 10 ³ Ω · cm ² on the surfaces of the developer-carrying member, the intermediate transfer member, and the transfer supporting member, which are roller-shaped members. An elastic layer made of a single polyurethane layer adjusted to ¹⁰ Ω · cm ² was provided. The elastic layer was adjusted to a thickness of 3 mm and a hardness of JIS-A hardness 50 °.

In Examples 9 to 22, an elastic layer made of a polyurethane layer having a thickness of 3 mm and a JIS-A hardness of 30 ° is provided on the surface of the developer carrying member, the intermediate transfer member, and the transfer supporting member. A polyurethane resin having a thickness of 30 μm and a JIS-A hardness of 85 ° was applied to form a resin layer. The amount of conductive filler added to the surface resin layer so that the electrical resistance per unit area of each member including both the elastic layer and the resin layer is 10 ³ Ω · cm ² to 10 ¹⁰ Ω · cm ^2. Adjusted. The electric resistance per unit area of the lower elastic layer was measured before applying the resin layer.

Note that paper (trade name: “OK Top Coat” (84 g / m ² ), manufactured by Oji Paper Co., Ltd.) was used as the recording medium. The electrical resistance per unit area of this paper was 10 ⁶ Ω · cm ² .

<Discharge unevenness>
The occurrence of discharge unevenness was evaluated by visually observing the image and ranked in the following two stages. A: Discharge unevenness does not exist on the image B: Discharge unevenness exists on the image.

<Granularity unevenness>
The occurrence of granular unevenness was evaluated by observing the solid part of the image at a magnification of 500 times using a microscope, and performing the following four ranks.

A: Toner particles are uniformly attached and the background is not visible B: Grain unevenness is slightly generated, but the background is not visible C: Particle unevenness is generated and the background is visible D: Granular unevenness Here, the background is a photosensitive member in development, an intermediate transfer member in primary transfer, and a recording medium in secondary transfer.

<Decrease in image density>
The presence or absence of a decrease in image density was evaluated by the following method. By preliminarily depositing toner particles uniformly on the recording paper and measuring the image density at this time using a reflection densitometer (trade name: “SpectroEye”, manufactured by X-Rite), the toner particle adhesion amount Create a calibration curve that shows the relationship between the image density and the image density. At the time of image formation, measure the mass of the liquid developer on the developer carrier, and multiply the mass by the solid content concentration (toner particle concentration) of the liquid developer. Thus, the adhesion amount of the toner particles on the developer carrier at the time of image formation is calculated. Then, the image density is calculated using the calibration curve. The image density thus obtained is referred to as an ideal image density. Next, in the output image, the image density of the solid portion is measured. Then, according to the percentage of the value obtained by dividing the image density of the output image by the ideal image density, the following three stages of ranking were performed to evaluate the presence or absence of a decrease in image density. The larger the value obtained in this way, the better the image density decrease is. A: 85% or more B: Over 75% and less than 85% C: 75% or less.

<Development efficiency and transfer efficiency>
Development efficiency and transfer efficiency were evaluated as follows. That is, after electrostatic transfer is performed at each part, the toner image remaining on the transfer-side roller and the toner image moved to the transfer-side roller are separated by a tape and collected, and the peeled toner image The transfer efficiency was calculated by measuring the image density using a reflection densitometer and dividing the image density on the receiving side by the image density on the passing side. As the tape, “Scotch Mending Tape” (trade name, manufactured by 3M) was used.

<Results and discussion>
<Development part>
Table 2 shows the test results in the developing section. In Comparative Example 1 using pulverized toner particles, no granular unevenness occurred regardless of the electric resistance of the developer carrier, but the development efficiency was less than 90%.

When the core / shell type toner particles are used, the effect of suppressing the movement of the toner particles is not sufficiently exhibited when the electric resistance of the developer carrier is 10 ³ Ω · cm ² and 10 ⁴ Ω · cm ² , and the granular unevenness There has occurred. In addition, it can be seen that the occurrence of granular unevenness tends to be smaller as the average circularity is lower and the median diameter is smaller (Comparative Examples 2, 4 and 6). On the other hand, when the electric resistance of the developer carrying member is set to 10 ⁵ to 10 ⁸ Ω · cm ² , the effect of suppressing the movement of the toner particles is exhibited and the occurrence of granular unevenness is small (practical) Examples 1-3). In Examples 1 to 3, the development efficiency was stable at a high value of 90% or more. That is, in Examples 1 to 3, both development efficiency and image quality were compatible.

  In Examples 1 and 2 in which a crystalline urethane-modified polyester resin was used as the core resin, the occurrence of granular unevenness could be suppressed almost completely, but an implementation using an amorphous resin as the core resin was possible. In Example 3, granular unevenness could not be completely suppressed. This is presumably because the average circularity tends to be high in the toner particles using an amorphous resin. Therefore, it is preferable to use a crystalline urethane-modified polyester resin as the core resin, and the average circularity of the toner particles is preferably 0.90 or more and 0.96 or less.

Further, when the resistance of the resistance layer exceeds 10 ⁹ Ω · cm, the occurrence of granular unevenness is not observed, but it seems that the charge on the surface of the developer carrying member is caused when images are continuously formed. Discharge unevenness occurred (Comparative Examples 1, 3, 5 and 7).

From these results, in order to suppress granular unevenness and also suppress other image noise, at least one of the two toner carriers for electrostatically transferring toner particles has a resistance against the surface. It is necessary that the resistance layer has an electric resistance of 10 ⁵ to 10 ⁸ Ω · cm ² . Therefore, the electric resistance of the resistance layer of the developer carrying member is preferably 10 ⁵ to 10 ⁸ Ω · cm ² .

<Primary transfer portion to secondary transfer portion>
Table 3 shows the test results at the primary transfer portion to the secondary transfer portion. In Comparative Example 8 using pulverized toner particles, no granular unevenness occurred regardless of the electrical resistance of the intermediate transfer member, but the transfer efficiency was less than 90%.

When the core / shell type toner particles are used, the effect of suppressing the movement of the toner particles is not sufficiently exerted when the electric resistance of the intermediate transfer member is 10 ³ Ω · cm ² or 10 ⁴ Ω · cm ² , and granular unevenness is caused. Occurred. At this time, the electrical resistance of the transfer support member was 10 ⁶ Ω · cm ² . It can also be seen that the occurrence of granular unevenness tends to decrease as the average circularity is lower and the median diameter is smaller (Comparative Examples 9, 11 and 13). In contrast, when the electric resistance of the intermediate transfer member is set to 10 ⁵ to 10 ⁸ Ω · cm ² , the effect of suppressing the movement of toner particles is exhibited, and the occurrence of granular unevenness is small (Example) 4-6). In Examples 4 to 6, the transfer efficiency was stable at a high value of 90% or more. That is, in Examples 4 to 6, it was possible to achieve both transfer efficiency and image quality.

Similarly to the above, in Example 3 in which an amorphous resin was used as the core resin, the granular unevenness could not be completely suppressed (Example 6). Further, when the electric resistance of the resistance layer of the intermediate transfer member exceeded 10 ⁹ Ω · cm, the mobility of the toner particles was excessively limited, and the transfer efficiency was remarkably reduced (Comparative Examples 10, 12 and 14).

From these results, it is preferable that the electric resistance of the resistance layer of the intermediate transfer member is 10 ⁵ to 10 ⁸ Ω · cm ² in order to suppress other image noise while suppressing the granular unevenness.

When the electric resistance of the intermediate transfer member was 10 ³ Ω · cm ² , granular unevenness occurred regardless of the electric resistance of the transfer supporting member (Comparative Example 15). This granular unevenness is considered to have occurred from the primary transfer portion. On the other hand, when the electric resistance of the intermediate transfer member was 10 ⁶ Ω · cm ² , no granular unevenness occurred (Example 7). However, when the electrical resistance of the transfer support member was 10 ⁹ to 10 ¹⁰ Ω · cm ² , the mobility of the toner particles was excessively limited, and the transfer efficiency was lowered. This is because the substantial transfer electric field in the secondary transfer is determined by the maximum resistance value among the intermediate transfer member, the transfer support member, and the paper. Therefore, in the secondary transfer portion, it is preferable that the member having the largest electrical resistance among the members related to the secondary transfer has an electric resistance of 10 ⁵ to 10 ⁸ Ω · cm ² .

<Influence of layer structure>
In order to investigate the influence of the configuration of the resistance layer, as shown in Table 4, development to transfer tests were performed by changing the layer configuration of the developer carrier, the intermediate transfer member, and the transfer support member.

  When the resistance layer of each roller was composed of a single layer, the granular unevenness was good, but the final image density was 80% of the ideal image density expected from the toner particle amount on the developer carrier. (Example 8). This is a result of a decrease in development efficiency and transfer efficiency due to insufficient electric field formation in the nip.

When the developer carrying member, the intermediate transfer member, and the transfer supporting member have the above-described multi-layer structure and have an electric resistance of 10 ⁵ to 10 ⁸ Ω · cm ² , generation of granular unevenness is suppressed and high The development efficiency and the transfer efficiency were ensured, and the decrease in image density could be reduced (Examples 10 and 13).

In Examples 9 and 11 in which the electric resistance of the developer carrying member is less than 10 ⁵ Ω · cm ² or more than 10 ⁸ Ω · cm ² , granular unevenness and discharge unevenness in the developing portion are reflected, and the final image is displayed. Noise appeared.

In Examples 12 and 14 where the electric resistance of the intermediate transfer member is less than 10 ⁵ Ω · cm ² or more than 10 ⁸ Ω · cm ² , the final image is reflected by the mobility of the toner particles in the primary transfer portion. Graininess and a decrease in image density appeared.

The developer carrying member, the intermediate transfer member, and the transfer supporting member have a multilayer structure, the electric resistance of the developer carrying member and the intermediate transfer member is 10 ⁵ to 10 ⁸ Ω · cm ² , and the electric resistance of the transfer supporting member is When it was 10 ⁸ Ω · cm ² or less, image formation was possible without causing a decrease in image density (Examples 15 and 16). However, when the electrical resistance of the transfer support member was too high, a decrease in image density was confirmed (Example 17).

  In Examples 18 to 20, the image density was higher than that in Example 8, but it was less than 85% of the ideal image density. In Example 18, since the intermediate transfer member was a single layer, the transfer efficiency slightly decreased in the primary transfer and the secondary transfer. In Example 19, since the developer carrier was a single layer, the development efficiency slightly decreased. In Example 20, since the electric resistance of the intermediate transfer member and the electric resistance of the paper were lower than the electric resistance of the transfer supporting member, it is considered that the efficiency was lowered during the secondary transfer. On the other hand, in Examples 21 and 22, an image having an ideal image density of 85% or more could be formed. This is because, in the secondary transfer portion, when the electrical resistance of the transfer support member is high, the transfer support member resistance layer is formed as a double layer, or when the intermediate transfer body has a high electrical resistance, the resistance layer of the intermediate transfer body is This is considered to be because the transfer efficiency was improved by using a multilayer.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Image carrier 2, Charging device 3, Exposure device, 4 Developing device, 5 Intermediate transfer body, 6 Transfer support member, 7 Image carrier cleaning device, 8 Intermediate transfer body cleaning device, 9 Developer carrier, 10 Eraser lamp , 11 recording medium, 12 liquid developer, 13 developer tank, 14 pumping member, 15 regulating blade, 16 supply member, 17 toner charging device, 18 developing cleaning member, 100 image forming apparatus.

Claims (8)

An image forming apparatus that forms an image on a recording medium using a liquid developer,
The liquid developer comprises toner particles dispersed in an insulating liquid,
The toner particles have an average circularity of 0.90 or more and 0.98 or less,
A first toner carrier for carrying the toner particles on the surface;
A second toner carrier disposed opposite to the first toner carrier and carrying the toner particles on the surface;
A power supply device for applying an electric field between the first toner carrier and the second toner carrier,
The first toner carrier has a resistance layer on a surface thereof, and an electric resistance per unit area of the resistance layer is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. . The toner particles have a core / shell structure in which a shell resin is attached to or coated on the surface of the core resin.
The image forming apparatus according to claim 1, wherein the shell resin includes a vinyl resin, and the vinyl resin has a long hydrocarbon chain in a side chain. The core resin is a urethane-modified polyester resin in which two or more polyester components are bonded by a structural unit derived from a compound having an isocyanate group,
The polyester component includes a structural unit derived from an aliphatic monomer in the molecular structure,
The image forming apparatus according to claim 2, wherein the structural unit derived from the aliphatic monomer occupies 80% or more of all the structural units in the polyester component. The image forming apparatus includes:
As the first toner carrier, a developer carrier,
The second toner carrier is disposed opposite to the developer carrier, and is developed by the toner particles carried by the developer carrier and forms a toner image on the surface thereof. The image forming apparatus according to any one of claims 1 to 3. The image forming apparatus includes:
As a third toner carrier, an intermediate transfer member that is disposed opposite to the image carrier and onto which a toner image formed on the surface of the image carrier is transferred,
A power supply device for applying an electric field between the image carrier and the intermediate transfer member,
The intermediate transfer member has a resistance layer on a surface thereof, and an electric resistance per unit area of the resistance layer is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. Image forming apparatus. The image forming apparatus includes:
A transfer support member disposed opposite to the image carrier with the recording medium interposed therebetween;
A power supply device for applying an electric field between the image carrier and the transfer support member,
The transfer assisting member has a resistance layer on its surface, and the larger of the electrical resistance per unit area of the resistance layer and the electrical resistance per unit area of the recording medium is 10 ⁵ Ω · cm ² or more and 10 The image forming apparatus according to claim 4, which is ⁸ Ω · cm ² or less. The image forming apparatus includes:
A transfer support member disposed to face the intermediate transfer member with the recording medium interposed therebetween;
A power supply device for applying an electric field between the intermediate transfer member and the transfer support member,
The transfer support member has a resistance layer on its surface,
Of the electrical resistance per unit area of the resistance layer of the intermediate transfer member, the electrical resistance per unit area of the resistance layer of the transfer support member, and the electrical resistance per unit area of the recording medium, the one having the largest value is The image forming apparatus according to claim 5, which is 10 ⁵ Ω · cm ² or more and 10 ⁸ Ω · cm ² or less. The resistance layer includes a plurality of layers,
The image forming apparatus according to claim 1, wherein an outermost surface layer of the plurality of layers has the highest electrical resistance value among layers included in the plurality of layers.

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